Semiconductor gain mediums have a short energy storage lifetime which makes energy extraction from the semiconductor gain medium less efficient compared with other gain mediums that have a longer energy storage lifetime. That is, a semiconductor optical amplifier is easily saturated and, after reaching the saturation regime, energy extraction from the semiconductor optical amplifier is dramatically decreased. It is well known that semiconductor optical amplifiers are not a proper optical amplifier for high power generation.
Previously, external cavity mode-locked semiconductor laser oscillators did not use dispersion management schemes that provide breathing mode operation. In non-breathing modes of operation, laser pulse time duration is similar at all cavity points. However, the preferable pulse duration, prior to a saturable absorber, is much shorter than pulse duration passing through the semiconductor gain media. Short pulses below ˜1 ps. bleach the saturable absorber much easier, but such short pulses would initiate different ultra-fast dynamic processes in gain media which are detrimental for the laser operation—the gain would be decreased and the pulse would be strongly nonlinearly chirped. The nonlinear chirp is very difficult to compensate and generate in the end ultrashort pulses.